1. Field of the Invention
The invention relates to a fuel injection system with pressure boosting for internal combustion engines.
2. Description of the Prior Art
A fuel injection system with pressure boosting, in which a central hydraulic pressure booster is provided for all the fuel injectors, is known from European Patent Disclosure EP 1 125 046 B1. The fuel pumped by means of a high-pressure pump is delivered to a central pressure reservoir (first common rail). The central pressure booster is connected downstream of the central pressure reservoir in the delivery direction of the fuel and delivers the pressure-boosted fuel to a further pressure reservoir (second common rail), from which a plurality of pressure lines corresponding to the number of injectors lead away the individual fuel injectors.
From European Patent Disclosure EP 1 123 463 B1, a further fuel injection system with pressure boosting is known. A central hydraulic pressure booster for all the fuel injectors is disposed in a bypass line parallel to a pressure line, which leads from the high-pressure pump to a distributor device, which in turn distributes the fuel to the various fuel injectors. However, the distributor device has no pressure storage function. The central pressure booster connected parallel is connected between the high-pressure pump and the distributor device.
A disadvantage of the pressure boosting systems is the high number of components needed as well as the relatively large control quantity for triggering the pressure booster. If for multiple injections of small injection quantities a boosted injection pressure is required, then the control chamber or differential pressure chamber of the pressure booster has to be relieved upon each injection. The result is a large control quantity that has to be diverted and that must accordingly be counted as a lost quantity in the injection system. Moreover, in terms of timing, multiple injections in the context of a cylinder stroke motion are possible only within a narrowly defined window, since each time the pressure booster is triggered, its differential pressure chamber has to refill with fuel. Moreover, with increasing injection pressures, the lost quantity increases in proportion to the fourth power across the gap width in the guide of the pressure booster piston, and this adversely affects the hydraulic efficiency of such fuel injectors.